Shared channel masks in on-product test compression system

ABSTRACT

A method of masking scan channels in a semiconductor chip includes storing, in first and second memories of a first mask logic, first and second channel mask enable decodes for first and second masks that mask first and second scan channels of a circuit under test; receiving at least three channel enable signals on three respective enable pins to produce a channel mask enable encode; comparing the channel mask enable encode to the stored first and second enable decodes; and masking the first or second scan channel when the channel mask enable encode respectively matches the first or second channel mask enable decode.

BACKGROUND

The present disclosure relates to testing electronic components, andmore specifically, to channel mask sharing in on-product testcompression (OPTC) systems.

Digital Integrated Circuits (ICs) can be prone to defects introducedduring a manufacturing process. These defects may affect the logicoutput of the digital IC, which in turn adversely influencessemiconductor chip quality and costs. Industry has developed a number oftesting techniques to test for the defects. To test for defects, an OPTCnetwork may be built into an IC, allowing the IC to test its ownoperations. OPTC networks may be implemented using hardware, software,or a combination of the two.

SUMMARY

According to embodiments of the present disclosure, a semiconductor chiphaving on-product test compression is disclosed as well as a designstructure of the same. The semiconductor chip includes a first masklogic. The first mask logic includes a first mask and a second mask thatmask a respective first scan channel output and a second scan channeloutput of a circuit under test. The first mask logic also includes atleast three channel mask enable pins. A first channel mask enable pinreceives a first channel mask enable signal. A second mask enable pinreceives a second channel mask enable signal. A third channel maskenable pin that receives a third channel mask enable signal. The threechannel mask enable signals produce a channel mask enable encode. Thefirst mask logic also includes a first memory that stores a firstchannel mask enable decode for the first mask and a second memory thatstores a second channel mask enable decode for the second mask. Thefirst mask logic includes a first comparator and a second comparator.The first comparator and second comparator compare the respectivechannel mask enable decodes to the channel mask enable encode. Thecomparators signal respective masks to mask the respective scan channelwhen the respective channel mask enable decode matches the channel maskenable encode.

In various embodiments, a method of masking scan channels in asemiconductor chip is described. The method includes storing, in a firstmemory of a first mask logic, a first channel mask enable decode for afirst mask that masks a first scan channel of a circuit under test. In asecond memory of a first mask logic, a second channel mask enable decodefor a second mask that masks a second scan channel of the circuit undertest is stored. The method includes receiving at least three channelmask enable signals. A first channel mask enable signal is received on afirst channel mask enable pin. A second channel mask enable signal isreceived on a second channel mask enable pin. A third channel maskenable signal is received on a third channel mask enable pin. The first,second, and third channel mask enable signals produce a channel maskenable encode. A first comparator compares the first channel mask enabledecode to the channel mask enable encode. A second comparator comparesthe second channel mask enable decode to the channel mask enable encode.The first scan channel is masked with the first mask when the firstchannel mask enable decode matches the channel mask enable encode. Thesecond scan channel is masked with the second mask when the secondchannel mask enable decode matches the channel mask enable encode.

The above summary is not intended to describe each illustratedembodiment or every implementation of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings included in the present application are incorporated into,and form part of, the specification. They illustrate embodiments of thepresent disclosure and, along with the description, serve to explain theprinciples of the disclosure. The drawings are only illustrative ofcertain embodiments and do not limit the disclosure.

FIG. 1 illustrates a high level block diagram of a semiconductor chiphaving a OPTC system, according to various embodiments.

FIG. 2 illustrates the mask logic with two mask bits for each scanchannel, according to various embodiments.

FIG. 3 illustrates a semiconductor chip having a plurality of hierarchaltest blocks (HTBs), according to various embodiments.

FIG. 4 illustrates a graphical representation of a method of sorting andcombining test patterns of various HTBs, according to variousembodiments.

FIG. 5 illustrates a flow diagram of a method that represents the methodgraphically illustrated in FIG. 4, according to various embodiments.

FIG. 6 illustrates circuit diagram of the mask logic of FIG. 1,according to various embodiments.

FIG. 7 illustrates the mask logic of FIG. 6 expanded to a plurality ofscan channels, according to various embodiments.

FIG. 8 illustrates a semiconductor chip with a plurality of HTBs usingmasking logic of FIG. 6, according to various embodiments.

FIG. 9 illustrates a graphical representation of a method of sorting andcombining test patterns of various HTBs, according to variousembodiments.

FIG. 10 depicts a flow diagram of a method of masking scan channels on asemiconductor chip, according to various embodiments.

FIG. 11 is a schematic block diagram illustrating a computer system,according to various embodiments.

FIG. 12 shows a block diagram of an exemplary design flow used forexample, in semiconductor IC logic design, simulation, test, layout, andmanufacture.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

DETAILED DESCRIPTION

Aspects of the present disclosure relate to testing electroniccomponents, more particular aspects relate to shared channel masks in anon-product test compression (OPTC) system and a method of sorting andcombining test patterns of hierarchal test blocks (HTB) of scan channelsto cycle patterns concurrently while minimizing over-masking. A mask isrequired when a scan channel latch produces and indeterminate alsoreferred to as an X-state result when a test pattern is cycled throughit. Masks may be shared between scan channels and HTBs. The sharing mayresult in over-masking where a mask is enabled for one scan channel orHTB that needs the mask but inadvertently masks good results from otherscan channels or HTBs. The method includes creating individual tests foreach unique HTB and sorting the patterns of each test into mask sets.The mask sets are defined by the number of masks each pattern requires.The mask sets of each are then combined to run concurrently in a waythat limits over-masking over different HTBs. Embodiments also includemask logic that can essentially increase the number of mask enables,which can be used in conjunction with the method to sort and combinemasks of HTBs in larger combinations to prevent over-masking. While thepresent disclosure is not necessarily limited to such applications,various aspects of the disclosure may be appreciated through adiscussion of various examples using this context.

FIG. 1 illustrates a high level block diagram of a semiconductor chip100 having an OPTC system and a test controller 104, according tovarious embodiments. The semiconductor chip 100 may include at least aspreading network 110, a circuit under test (CUT) 113, mask logic 120,and an output response analyzer (ORA) 125. The test controller 104 maybe in communication the spreading network 110, the CUT 113, channel masklogic 120, and ORA 125. The test controller 104 may include modules usedto control the components of the test including the channel mask logic120 and may also provide the test patterns for the semiconductor chip100. The spreading network 110 may spread the test patterns to aplurality of scan channels 115 within the CUT 113. Each scan channel 115may include a plurality of scan latches. When a test pattern enters thescan channels a scan output may be produced from the scan channels 115and sent to an ORA 125 to determine whether the CUT 113 is functioningproperly. The ORA 125 may include a multiple input signature register(MISR). The MISR may compress the scan outputs for each pattern toproduce a scan signature which may be compared to a predicted signature.If the signatures are identical, then the CUT 113 functions properly.

However, certain scan latches of the scan channels 115 may outputunknown results, also referred to as X-states herein, to the multipleinput signature register (MISR) or an on-product multiple inputsignature register (OPMISR). In a MISR-based compaction scheme, thepresence of a single X-state in any on of the scan channels mayinvalidate the MISR signature once it is captured. Every MISR signaturecaptured after that scan cycle may be unpredictable as well and theresults may have to be excluded from the test coverage calculations. InFIG. 1, block 130 in scan channel(0), block 132 in scan channel(1),block 134 in scan channel(2), and block 136 in scan channel(3) representlatches of each scan channel that produce an X-state from a particulartest pattern. Scan channel(4)-scan channel(31) may have scan latchesthat do not produce any X-states for the test pattern.

Channel mask logic 120 may be included in the BIST system, which maymask the unknown X-state test results of the scan outputs with validresults before the scan outputs enter the MISR for compression. Oneimplementation of mask logic 120 includes two mask-bits per channel andit also utilizes two streams of channel mask enable (CME) data storedoff-chip or with the test controller 104. The CME data may be controlledby two channel mask enable signals CME0 and CME1 on two respective CMEpins. Cumulatively, this provides four possible states: threechannel-masking states and one non-masking state. The threechannel-masking states may be a first unique mask, a second unique mask,and a mask all inputs. For instance, when CME0 is a logical one and CME1is a logical zero the first unique mask may be active. When CME0 is alogical zero and the CME1 is a logical one the second unique mask may beenabled. When both CME0 and CME1 are logical ones, then an entire scanslice may be masked. When both CME0 and CME1 are logical zeros, then nomask may be enabled. The CME pins may switch to a new state on each scancycle for each scan slice.

FIG. 2 illustrates the mask logic 120 with two mask bits for each scanchannel 115, according to various embodiments. The mask logic 120 mayinclude a first mask 205 and a second mask 210. An output of a firstmask (M1) 205 signals a first input of a NAND gate 220. A first channelmask enable CME0 may signal a second input of the NAND gate 220, a firstinput of a NAND gate 225 and feed an inverted input to NAND 230. Asecond mask (M2) 210 may signal a first input of a NAND gate 230. Asecond channel mask enable CME1 may signal a second input of NAND gate225, a second input of NAND gate 230 and feed an inverted input toNAND220. An AND gate 215 may receive a scan output from the scan channel115 at a first input, an output of the NAND gate 220 at a second input,an output of the NAND gate 225 at a third input, and an output of theNAND gate 230 at a forth input. Each scan channel in the CUT 113 of FIG.1 may have an AND gate like AND gate 215 where a first input of each ANDgate may receive a respective scan outputs. The other inputs of the ANDgates may receive the outputs of the NAND gates like NAND gates 220 and230, which means they may share the channel mask enables CME0 and CME1and NAND gate 225.

Different CME signals may determine which mask to use and whether a maskshould be used or not for a scan slice. When both CME0 and CME1 arelogical ones, then all scan channels of the scan output are masked atthat time. When both CME0 and CME1 are logical zeros, then there are nomasks in the current scan slice that is the scan output. If CME0 is alogical one and CME1 is a logical zero, then the scan channels 115 aremasked when the first mask 205 has a logical one for a particular scanchannel 115. If the first mask 205 has a logical zero for a specificscan channel, those scan channels remain unmasked. Likewise, if CME0 isa logical zero and CME1 is a logical one, then the scan channels 115 aremasked when the second mask 210 has a logical one for a particular scanchannel. If the second mask 210 has a logical zero for a specific scanchannel, those scan channels remain unmasked.

Having the four possible mask states works well in situations wherethere is a good circuit design not requiring a lot of masking. However,when a circuit under test such as CUT 113 requires a lot of masking orwhen performing hierarchical testing (discussed below), over-masking mayoccur as a result of the limited enables. When a CUT requires a lot ofmasking due to a large number of scan latches with X-states, thenover-masking, also referred to as false masking herein, may occur.

An example of false masking may be shown with respect to FIG. 1. Block130 of scan channel(0) represents an X-state. The masking logic 120 maybe adapted to mask block 130 with the first unique mask when CME1 andCME0 signal a respective ‘01’. Block 132 of scan channel(1) and block136 of scan channel(3) may be X-states in the same scan slice.Therefore, the mask logic 120 may be adapted to mask both blocks 132 and136 with the second unique mask when CME1 and CME0 signal a respective‘10’. Both blocks 132 and 136 may be masked leaving the latches withinthe scan slice of the remaining scan channels to be unmasked. At thispoint, both the first unique mask and the second unique mask have beenused. However, there is a remaining block, block 134 of scan channel(2),which produces an X-state.

One of the unique masks may need to be used to mask block 134. This iswhere false masking may occur. Since two scan channels are sharing thesecond unique mask, the first unique mask may be chosen to mask block134. However, since scan channel(0) uses that mask as well, when thefirst unique mask is enabled for block 134 it is also going to mask ablock of scan channel(0) that is in the same scan slice as block 134,which does not produce an X-state in this example. Also, since both scanchannel(0) and scan channel(2) are sharing the first unique mask, whenthe mask is enabled for block 130 in scan channel(0), then it is alsoenabled for the block in the same scan slice of block 130 for scanchannel(2), which may not produce an X-state. These over-masked validresponses may not be included in the test data received by the MISRreducing the quality of the test.

Some over-masking may be acceptable. Over-masking is not always going tolead to loss of test coverage when the over-masking is limited. However,in circuits requiring heavy masking or implementing a hierarchal test,over-masking can limit test coverage to a point where it is a burden.Hierarchal testing may be dividing the scan channels 105 of the CUT 103into smaller areas or groups that may be tested independently. Each areamay be referred to as a hierarchal test block (HTB). Each HTB may haveits test generated independently to allow a smaller test model and lowerprocessing time. In current methodologies, both mask data and the CMEpins are shared between the HTBs, so either each HTB must be testedindependently or a larger model created that combines multiple HTBs fortest generation. The creation of a larger model somewhat defeats thepurpose of the hierarchal test.

The more HTBs that are combined, the more false masking may occur. Thisis because the HTBs share the masks and CME signals. For example, afirst HTB may be tested concurrently with a second HTB. At a particularscan cycle, the first HTB may need a mask such as the first mask 205 ina scan slice (one cycle scan data across all scan outputs). When themask is triggered for the first HTB it will also be triggered for thesecond HTB since they may share the same CME signals such as CME0signaling a logical 1 and CME1 signaling a logical zero. The mask in thesecond HTB may not be needed for that scan slice. The mask, the secondHTB receives, may be defined for use on a different scan slice in thesame test. So when the mask for the second HTB is triggered, it maytrigger a false mask in the first HTB as well. Adding two CME inputs foreach HTB and more masks may solve this dilemma. However, hardwareoverhead and usage of more test input resource makes this option costlyin performance of the test and chip space. A procedure for patterncompression when performing hierarchal test is presented in variousembodiments of this disclosure. Furthermore, an encoding scheme that canmore focus masking on an HTB that needs it is also presented in variousembodiments of this disclosure. These embodiments may allow for use ofsmaller individual HTB models for quicker processing, limit falsemasking that results in less coverage loss, and creates fewer testpatterns saving test time or allowing more patterns for better testcoverage.

FIG. 3 illustrates a semiconductor chip 300 having a plurality ofhierarchal test blocks (HTBs), according to various embodiments. In theexample shown in FIG. 3 there are five HTBs: HTB A 305, HTB A 310, HTB B315, HTB B 320, and HTB C 325. Combining HTBs that are identical such asthe HTB A 305 and 310 and HTB B 315 and 320 may be free in that they canshare the same scan inputs and mask encodes. In FIG. 3 there are threeunique HTBs: HTB A, HTB B, and HTB C. A scan input signal SI(1) mayinput into the HTB A 305 and 310. Each may output a scan output SO(1).HTB A 305 and 310 may be masked by a first mask M1 that may be assignedto a CME encode of (01) from CME1 and CME0, respectively, and by asecond mask M2 that may be assigned to a CME encode (10) from CME1 andCME0, respectively. The CME encodes may signal when their respectivemasks are to be enabled.

A scan input signal SI(2) may input into the HTB B 315 and 320. Each mayoutput a scan output SO(2). HTB B 315 and 320 may be masked by a firstmask M1 that may be assigned a CME encode of (01) from CME1 and CME0,respectively, and by a second mask M2 that may be assigned a CME encode(10) from CME1 and CME0, respectively.

A scan input signal SI(3) may input into the HTB C 325. HTB C 325 mayoutput a scan output SO(3). HTB C 325 may be masked by a first mask M1that may be assigned a CME encode of (01) from CME1 and CME0,respectively, and by a second mask M2 that may be assigned a CME encode(10) from CME1 and CME0, respectively.

Each of the unique HTBs may require 1000 patterns for their independenttests. As stated before, each HTB is currently tested serially, whichmeans that if HTB A, HTB B, and HTB C have 1000 patterns each for theirtest, the total number of patterns tested would be 3000. Running thepatterns concurrently may present over masking issues as stated before.Furthermore, mask loading for every pattern can take a large part of thetest time and data volume. Various embodiments herein describe a methodof combining and sorting patterns of the HTBs that have similar maskingneeds to reduce data volume and test time.

FIG. 4 illustrates a graphical representation of a method of sorting andcombining test patterns of various HTBs, according to variousembodiments. The test patterns for an HTB may be sorted out into groupsof two, one, or zero mask sets. For example, a two mask set needs bothmasks M1 and M2 for the test patterns within it. A one mask set needsone of the masks for its patterns. A zero mask set may need no masks forits patterns. Table 405 illustrates the HTBs of FIG. 3 and the testpattern count per mask set for an illustrative example. HTB A may have300 test patterns that need the two mask set, 400 test patterns thatrequire the one mask set, and 300 test patterns that require the zeromask set. HTB B may have 400 patterns that require the two mask set, 300patterns that require the one mask set, and 300 patterns that requirethe zero mask set. The HTB C may have 200 patterns that require the twomask set, 500 patterns that require the one mask set, and 300 patternsthat require the zero mask set. A mask pattern module sorting thepatterns may know where the latches are within the scan channels thatproduce X-state results. The mask pattern module may know from thepatterns it produces or from the test patterns a built in testerproduces which patterns will need a certain number of masks. In thisexample, it is assumed that a test pattern is not going to be completelymasked with a CME0 and CME1 encode of (11). The mask pattern module maybe computer program product or physical logic that may perform themethod of sorting and combining test patterns of various HTBs of thesemiconductor chip. The mask pattern module may be stored in memory andexecuted by a processor either on or off the semiconductor chip 100according to various embodiments. The mask pattern module is furtherdescribed below in FIG. 11.

Once the patterns are sorted, the mask pattern module may combine thegroups of patterns from the various HTBs so that not more than thegreatest number of mask encodes are used for a combined test pattern. Inthe chart 410, by using the information in table 405, the mask patternmodule may align the HTB patterns requiring the two mask patternsserially because the maximum number of mask encodes is two. If the maskpattern module aligned the HTB patterns requiring two mask patterns oreven patterns requiring one mask pattern together in the same scanslice, then false masking may occur across HTBs. Therefore, the two masksets of the HTBs are serial and are padded with zero mask sets of theother HTBs. Padded means that the test patterns of one HTB are combinedwith test patterns of another HTB so that they may cycle concurrently.In chart 410, patterns of HTB A with two mask sets A(2) may be the first300 patterns performed, patterns of HTB B with two mask sets B(2) may bethe next 400 patterns performed, and patterns of HTB C with two masksets C(2) may be the next 200 patterns performed. While each of the twomask sets of the HTBs are performed, patterns requiring zero masks ofother HTBs may pad the patterns that require two masks. Therefore,essentially 1800 patterns from the two mask set and the zero mask set oftable 405 are reduced to 900 patterns. Also, since more zero mask setpatterns can be used to pad the two mask set patterns than what HTB A,HTB B, and HTB C originally had, then the zero mask set patterns may berepeated or other zero mask set patterns may be added to the test.

After the two mask set patterns have been combined with the zero maskset patterns, then the one mask set patterns may be combined. The maskpattern module may pad the largest one mask set with the next largestmask set. The zero mask set of the remaining HTB may be padded also withthe two one mask sets. The remaining mask set or the mask set with theleast number of patterns may begin once the mask set with the nextlargest pattern count finishes.

For example, chart 410 continues at pattern 900. The largest one maskset, C(1), begins at pattern 900. The next largest mask set, A(1) may bepadded with C(1). Since A(1) and C(1) only need one mask each, then theymay be combined without over-masking. The remaining HTB B may pad A(1)and C(1) with B(0) zero mask set patterns. Once A(1) finishes at pattern1300, then B(1) may begin, which will end at pattern 1600 and be paddedwith the remaining C(1) mask sets patterns and with A(0) and C(0) maskset patterns. Sorting and combining mask sets of the different HTBsreduces the number of patterns from 3000 to 1600 in this example.Furthermore, in this example, the total number of zero mask set patternstested may be increased from 900 to 2700 patterns.

FIG. 5 depicts a flow diagram of a method 500 that represents the methodgraphically illustrated in FIG. 4, according to various embodiments. Inoperation 505, the independent tests may be generated for each uniqueHTB on the semiconductor chip. In operation 510, the mask pattern modulemay sort the patterns of each HTB test into mask sets. Each mask set maybe the number of masks each pattern requires. Zero, one, and two masksper pattern may be the possible numbers of masks per pattern. However,other mask quantities may be contemplated per pattern. A maximum numberof masks may be contemplated. The sorting may be done from mask setsrequiring zero masks to the maximum mask set.

In operation 515, the mask pattern module may serialize the two masksets meaning one will begin when another ends. In other embodiments, ifthe number of mask encodes is greater than two, then other two mask setsmay be combined or other various numbered mask sets may be combined withthe up to the number of mask encodes on the chip. For instance if thereare 3 mask encodes, then a two mask set may be combined with a one maskset and performed in parallel. The numbered mask set must be no morethan the number of encodes available.

In operation 520, once the two mask sets have been serialized they maybe padded with zero mask sets from remaining HTBs. The zero mask setpatterns may be repeated even after they have already been padded withother mask sets.

In operation 525, mask pattern module may determine whether a one maskset with the second most patterns is greater than zero patterns. If theone mask set with the second most patterns has more than zero patterns,then in operation 530 the one mask set with the second most patterns maybe selected. In operation 535, the one mask set with the second mostpatterns may be padded with a one mask set having the most patterns. Inoperation 540, the CME and mask may be adjusted so one mask sets thatare combined have separate encodes. The one mask set patterns performedin parallel may be padded with unrepresented HTBs zero mask sets. TheHTB patterns with zero mask sets may be repeated more than once, ifneeded. In operation 545 the pattern count of both one mask sets(largest pattern one mask set and second largest pattern one mask set)may be decremented to second most pattern count of one mask sets.

In operation 560, the mask pattern module may determine whether any onemask sets with pattern counts that are greater than zero remainuncombined. If there are one mask sets with pattern counts greater thanzero, then the method 500 may return to operation 525 where it isdetermined whether the one mask set with the second most patterns has apattern count greater than zero patterns. If it is not greater thanzero, then in operation 655 the mask pattern module may select theremaining one mask set and pad it with zero mask sets. The zero masksets may be used again, if they were used in combination with other masksets. In operation 560, once all one mask sets have been combined, thenany remaining zero mask sets may be combined. In operation 565, afterall of the mask sets have been sorted and combined, the combined masksets may be stored as a scan pattern test file to be executed whentesting HTBs. In various embodiments, the scan pattern test file may beexecuted by the test controller 104 of FIG. 1. In other embodiments thescan pattern test file may be executed by device in communication withthe semiconductor chip being tested.

FIG. 6 depicts circuit diagram of mask logic 600, according to variousembodiments. Mask logic 600 may be a representative embodiment of masklogic 120. The mask logic 600 may be used separate or in conjunction tothe method 500 above to allow use of smaller individual HTB models forquicker processing, avoiding false masking, and creating few testpatterns. The mask logic 600 essentially increases the number of masksand mask encodes without increasing the physical number of masks andwithout creating separate channel mask enables for each HTB.

The mask logic 600 may receive three CME inputs, a CME0, CME1, and CME2.The CME inputs may signal a respective first, second and third input ofa NAND gate 605. The output of NAND gate 605 may couple to a secondinput of AND gate 610, which signals the output of a scan channel 115 toa MISR. The output of the scan channel 115 may be coupled to a firstinput of the AND gate 610. AND gate 610 may output a logical 0 when thescan channel outputs a logical 0. The AND gate 610 may output a logical1 when the scan channel outputs a logical 1. The AND gate 610 may outputwhatever the scan channel 115 outputs unless a mask is enabled.

The three CME inputs: CME0, CME1, and CME2 may create eight encodesinstead of the four created when there were two CME inputs, e.g., FIG.2. When CME0, CME1, and CME2 are all logical ones, then the mask logic600 masks all scan channels for the scan slice that all CME inputs areenabled. This may be represented by the NAND gate 605. When the CMEinputs are all logical zeros, then no mask may be enabled. Six maskenable signals then remain, when taking into account the mask all encodeand the no mask encode, compared to two when there are two CME inputs.

The mask logic 600 may also include a first mask 615 and a second mask620. The output of the first mask may be coupled to a first input of aNAND gate 625. The output of the second mask may be coupled to a firstinput of a NAND gate 630. The outputs of NAND gate 625 and NAND gate 630may be coupled to a third input and fourth input, respectively, of theAND gate 610.

The mask logic 600 may include two programmable decodes in a memory suchas a register: a first memory 635 storing a first decode and a secondmemory 640 storing a second decode. The first decode may be compared ina first comparator 645 with the encode from the CME inputs. If the CMEencode and first decode matches, then first comparator 645 may signal asecond input of the NAND gate 625. This may enable the first mask 615.Likewise, a second decode in the second memory 640 may be compared witha second comparator 650 to the CME encode from the CME inputs. If theCME encode matches the second decode, then the second comparator 650 maysignal a second input of the NAND gate 630. This may enable the secondmask. In various embodiments, each scan channel 115 of a CUT 113 may beenabled with one of the six encodes, which may greatly reduce falsemasking without using a large amount of area on the chip with extramasks.

FIG. 7 illustrates the mask logic 600 of FIG. 6 expanded to other scanchannels 115, according to various embodiments. In this example eachscan channel(0) and scan channel(1) may have two decodes. Scanchannel(0) may have the first memory 635 having first decode and thesecond memory 640 having the second decode. The first decode may be fora CME encode of (001) where CME2 inputs a logical zero, CME1 inputs alogical zero, and CME0 inputs a logical one. The second decode may befor a CME encode of (010) where CME2 inputs a logical zero, CME1 inputsa logical one, and CME0 inputs a logical zero.

Likewise, scan channel(1) may have a third memory 705 and a fourthmemory 710 with a respective third decode and fourth decode. The thirddecode may be for a CME encode of (011) where CME2 inputs a logicalzero, CME1 inputs a logical one, and CME0 inputs a logical one. Thefourth decode may be for a CME encode of (100) where CME2 inputs alogical one, CME1 inputs a logical zero, and CME0 inputs a logical zero.

In operation, the CME inputs may signal throughout pattern testing foreach scan cycle, when a CME encode matches a decode of the variousmemories 635, 640, 705, and 710. For instance, when a CME encode of(100) is received by the mask logic 600, the second mask 745 may beenabled for the scan channel(1). When a CME encode (010) is received bythe mask logic 600, the second mask 620 may be enabled for the scanchannel(0). When a CME encode of (001) is received by the mask logic600, the first mask 615 may be enabled for the scan channel(0). When aCME encode of (011) is received by the mask logic 600, the first mask740 may be enabled for the scan channel(1). This may decreaseover-masking since two x-states on scan channel(0) may be independentlymasked from two x-states on scan channel(1). One caveat is that scanchannels having an x-state within the same scan slice may have to havetheir decodes match so that they may be masked at the same time.

In other various embodiments, each HTB may be assigned one or moreunique encodes (perhaps zero encodes when no masking is needed in theHTB) to enable the first mask 625 and the second mask 630 of FIG. 6 forthe scan channels 115 within the HTB. This may reduce the false maskingacross HTBs and also decrease test patterns when sorting and combiningtest patterns of multiple HTBs due to being able to combine more testpatterns from individual HTBs to run together in a scan cycle.

FIG. 8 depicts a semiconductor chip 800 having a plurality of HTBs usingmasking logic 600, according to various embodiments. In the exampleshown in FIG. 8 the semiconductor chip 800 has eight HTBs, six of whichare unique HTBs using the masking logic 600. The number of HTBs may beany number of HTBs, the number of HTBs in FIG. 8 represents an example,according to various embodiments. In the example shown in FIG. 8 thereare eight HTBs: HTB A 805, HTB A 810, HTB B 815, HTB B 820, HTB C 825,HTB D 830, HTB E 835, and HTB F 840. Combining HTBs that are identicalsuch as the HTB A 805 and HTB A 810 and HTB B 315 and HTB B 320 may befree in that they can share the same scan inputs and mask encodes. InFIG. 8 there are six unique HTBs, A, B, C, D, E, and F. A scan inputsignal SI(1) may input into the HTB A 805 and 810. Each HTB A 805 and810 may output a scan output signal SO(1). HTB A 805 and 810 may bemasked by a first mask M1 that may be assigned a CME encode of (001)from CME2, CME1 and CME0 respectively and by a second mask M2 that maybe assigned a CME encode (010) from CME2, CME1 and CME0, respectively.In various embodiments, the assigned CME encode in the registers foreach HTB may change from pattern to pattern, so while HTB A and HTB Dmatch in this example, they may be assigned different encodes in anotherpattern.

A scan input signal SI(2) may signal the HTB B 815 and 820. HTB B 815and 820 may output a scan output signal SO(2). HTB B 815 and 820 may bemasked by the first mask M1 that may be assigned a CME encode of (011),which enables the mask, from CME2, CME1 and CME0, respectively and bythe second mask M2 that may be assigned a CME encode (100) from CME2,CME1 and CME0, respectively.

A scan input signal SI(3) may input into the HTB C 825. HTB C 825 mayoutput a scan output signal SO(3). HTB C 825 may be masked by the firstmask M1 that may be assigned a CME encode of (101) from CME2, CME1, andCME0, respectively and by the second mask M2 that may be assigned a CMEencode (110) from CME2, CME1 and CME0, respectively.

A scan input signal SI(4) may input into the HTB D 830. HTB D 830 mayoutput a scan output signal SO(4). HTB D 830 may be masked by the firstmask M1 that may be assigned a CME encode of (001) from CME2, CME1, andCME0, respectively and by the second mask M2 that may be assigned a CMEencode (010) from CME2, CME1 and CME0, respectively. HTB D may share thesame two mask encodes as HTB A. In various embodiments, HTB D may sharethe first mask encode of HTB A and share a second mask encode of adifferent HTB such as HTB B(100) or HTB C (110).

A scan input signal SI(5) may input into the HTB E 835. HTB E 835 mayoutput a scan output signal SO(5). HTB E 835 may be masked by the firstmask M1 that may be assigned a CME encode of (011) from CME2, CME1, andCME0, respectively and by the second mask M2 that may be assigned a CMEencode (100) from CME2, CME1 and CME0, respectively. HTB E may share thesame two mask encodes as HTB B in this example.

A scan input signal SI(6) may input into the HTB F 840. HTB F 840 mayoutput a scan output signal SO(6). HTB F 840 may be masked by the firstmask M1 that may be assigned a CME encode of (101) from CME2, CME1, andCME0, respectively and by the second mask M2 that may be assigned a CMEencode (110) from CME2, CME1 and CME0, respectively. HTB F may share thesame two mask encodes as HTB C in this example.

Each of the unique HTBs may require 1000 patterns for their ownindependent test. As stated before, each HTB may be tested serially,which means that if HTB A, HTB B, HTB C, HTB D, HTB E, and HTB F have1000 patterns each for their test, the total number of patterns testedwould be 6000. Running the patterns concurrently may present overmasking issues as stated before. Furthermore, mask loading for everypattern can take a large part of the test time and data volume.Addressing the HTBs with different CME encodes, may reduce over-maskingof scan slices over HTBs.

While having separate scan inputs for each HTB helps with independenttest pattern generation, sharing test patterns by sharing the same scaninput may allow for more patterns to be applied in less time. Forinstance, the test patterns created for HTB A may be applied to HTB Bwhen tested for HTB A and test patterns created for HTB B may be appliedto HTB A when tested for HTB B. Although the test patterns may not begenerated for the specific HTB they may still provide test coverage.When using the two mask encode system, a scan slice of HTB B which maynot have a scan latch with an unknown state may get masked when a scanlatch of HTB A is masked for the HTB A test patterns. Having thedifferent CME encodes for each HTB may prevent over-masking of HTB Bwhen masking HTB A and vice versa. Additional masking may be created forHTB B when running the HTB A encodes, so the different CME encodes foreach HTB may allow for independent masking of the HTBs.

FIG. 9 illustrates a graphical representation of a method of sorting andcombining test patterns of various HTBs, according to variousembodiments. All of the patterns for an HTB may be sorted out intogroups of two, one, or zero mask sets. For example, patterns of two masksets need both masks M1 and M2 for the pattern. Patterns of one masksets need one of the masks. Patterns of zero mask sets may need nomasks. Table 905 illustrates the HTBs of FIG. 8 and the pattern countper mask set for an illustrative example. HTB A has 300 patterns thatneed two mask sets, 400 patterns that require one mask set, and 300patterns that require zero mask sets. HTB B may have 400 patterns thatrequire the two mask set, 300 patterns that require one mask set, and300 patterns that require zero mask sets. The HTB C may have 200patterns that require two mask sets, 500 patterns that require one maskset, and 300 patterns that require zero mask sets. The HTB D may have300 patterns that require two mask sets, 400 patterns that require onemask set, and 300 patterns that require zero mask sets. The HTB E mayhave 400 patters that require two mask sets, 300 patterns that requireone mask set, and 300 patterns that require zero mask sets. The HTB Fmay have 200 patterns that require two mask sets, 500 patterns thatrequire one mask set, and 300 patterns that require zero mask sets. Amask pattern module sorting the patterns may know where the latches arewithin the scan channels that produce X-state results. The mask patternmodule may know from the patterns it produces or from that a built intester produces which patterns will need a certain number of masks. Inthis example, it is assumed that all latches across a scan slice for allHTBs are not going to be completely masked with a CME2, CME1, and CME0encode of (111).

Once the patterns are sorted the mask pattern module may combine thegroups of patterns from the various HTBs so that not more than thegreatest number of mask encodes are used for a particular scan slice. Inthe chart 910, by using the information in table 905, the mask patternmodule may align the test patterns of the HTBs requiring two mask setstogether up to the maximum number of CME encodes. Because there are sixdifferent encodes, testing with patterns that require up to six“different masks” are allowed. Therefore, when each HTB has a maximum oftwo CME encodes, three HTBs having different CME encodes may becombined. In the given example HTB A(2), HTB B(2), and HTB C(2) patternsmay be combined and begin at zero. These HTBs with the two mask setpatterns may be padded with remaining zero mask set patterns of theremaining HTBs: HTB D(0), HTB E(0), and HTB F(0). In chart 910, HTB A(2)may be the first 300 patterns performed, HTB B(2) may performconcurrently 300 of its 400 patterns, and C(2) may perform concurrentlyits 200 patterns. While each of these are two mask pattern sets areperformed, patterns requiring zero masks may pad the patterns thatrequire two masks. Therefore, essentially 1800 patterns from the twomask sets and the zero mask sets of table 905 are reduced to 400patterns which is the longest two mask set, HTB B(2).

After the patterns of the two mask sets have been combined with thepatterns of the zero mask sets, then the one mask set patterns may becombined. The mask pattern module may pad the largest one mask set withthe next largest mask set and so on up to the maximum number of encodes.Since there are six CME encodes, then there may be six HTB one mask setsrunning concurrently. The zero mask set of the remaining HTBs may bepadded also with the one mask sets. For example, in chart 910 thelargest one mask set C(1) may follow the C(2) patterns at pattern count200. From pattern count 200 to 300 A(2), B(2), and C(1) may runtogether, which means there are only 5 CME encodes being used duringthat time. A(1), D(1), and F(1) may begin at pattern count 300. Thisincreases the number of encodes used to six. Thus, E(1) is chosen not torun until more CME encodes are available after B(2) finishes. The gapbetween E(0) and E(1) may be filled with repeated E(0) patterns invarious embodiments. Once the one mask sets finish the remaining twomask sets (D(2), E(2), and F(2)) may begin. The two mask sets D(2) andE(2) may begin at pattern 700 while F(2) may begin at pattern count 800.D(2) and F(2) may end at pattern count 1000 as well as the zero masksets. The two mask set E(2) may be completed at pattern count 1100.Repeated zero mask sets or a combination of zero, one, and two mask setsmay be used from pattern 1000-1100 while E(2) is finishing, according tovarious embodiments.

FIG. 10 depicts a flow diagram of a method 1000 of masking scan channelson a semiconductor chip, according to various embodiments. In operation1005, a first CME decode assigned to a first mask that masks a firstscan channel may be stored in a first memory. In operation 1010,likewise, a second CME decode assigned to a second mask that masks asecond scan channel may be stored in a second memory. In operation 1015,at least three CME signals may be received that produce a CME encode. Afirst CME signal may be received on a first CME pin. A second CME signalmay be received on a second CME pin. A third CME signal may be receivedon a third CME pin. The three signals may make up the CME encode.

In operation 1020, the first CME decode may be compared to the CMEencode with a first comparator. In operation 1025, the second CME decodemay be compared to the CME encode with a second comparator. In operation1030, the first scan channel may be masked with the first mask when thefirst CME decode matches the CME encode. In operation 1035, the secondscan channel may be masked with the second mask when the second CMEdecode matches the CME encode.

While the Detailed Description may refer to specific types oftransistors, logic gates, supply voltages, and the like it will beappreciated that one skilled in the art may implement same or similarfunctions using different transistors, logic gates, and supply voltagesin alternative embodiments as described and still accomplish the samepurpose of the invention. For example, transistors may be PFETs orNFETs. Logic gates may be AND, OR, XOR, NOR, NAND, XNOR or inverters.Therefore, the scope of the invention should not be limited.

FIG. 11 is a schematic block diagram illustrating one embodiment of acomputer system 1100. The computer system 1100 is one exemplary contextin which embodiments may be implemented. The mechanisms and apparatus ofthe various embodiments disclosed herein apply equally to anyappropriate computing system. The major components of the computersystem 1100 include one or more processors 1102, a memory 1104, aterminal interface 1112, a storage interface 1114, an Input/Output(“I/o”) device interface 1116, and a network interface 1118, all ofwhich are communicatively coupled, directly or indirectly, forinter-component communication via a memory bus 1106, an I/O bus 1108,bus interface unit (“IF”) 1109, and an I/O bus interface unit 1110.

The computer system 1100 may contain one or more general-purposeprogrammable central processing units (CPUs) 1102A and 1102B, hereingenerically referred to as the processor 1102. In an embodiment, thecomputer system 1100 may contain multiple processors; however, inanother embodiment, the computer system 1100 may alternatively be asingle CPU system. Each processor 1102 executes instructions stored inthe memory 1104 and may include one or more levels of on-board cache.

In an embodiment, the memory 1104 may include a random-accesssemiconductor memory, storage device, or storage medium (either volatileor non-volatile) for storing or encoding data and programs. In anotherembodiment, the memory 1104 represents the entire virtual memory of thecomputer system 1100, and may also include the virtual memory of othercomputer systems coupled to the computer system 1100 or connected via anetwork 1140. The memory 1104 is conceptually a single monolithicentity, but in other embodiments the memory 1104 is a more complexarrangement, such as a hierarchy of caches and other memory devices. Forexample, memory may exist in multiple levels of caches, and these cachesmay be further divided by function, so that one cache holds instructionswhile another holds non-instruction data, which is used by the processoror processors. Memory may be further distributed and associated withdifferent CPUs or sets of CPUs, as is known in any of various so-callednon-uniform memory access (NUMA) computer architectures.

The memory 1104 may store all or a portion of the following: maskpattern module 1130 and a scan pattern test file 1132. These programsand data structures are illustrated as being included within the memory1104 in the computer system 1100, however, in other embodiments, some orall of them may be on different computer systems and may be accessedremotely, e.g., via a network 1130. The computer system 1100 may usevirtual addressing mechanisms that allow the programs of the computersystem 1100 to behave as if they only have access to a large, singlestorage entity instead of access to multiple, smaller storage entities.Thus, while the mask pattern module 1130 and a scan pattern test file1132 are illustrated as being included within the memory 1104, thesecomponents are not necessarily all completely contained in the samestorage device at the same time. Further, although mask pattern module1130 and a scan pattern test file 1132 are illustrated as being separateentities, in other embodiments some of them, portions of some of them,or all of them may be packaged together.

In an embodiment, mask pattern module 1130 and a scan pattern test file1132 may include instructions or statements that execute on theprocessor 1102 or instructions or statements that are interpreted byinstructions or statements that execute on the processor 1102 to carryout the functions as further described below. In another embodiment,mask pattern module 1130 and a scan pattern test file 1132 may beimplemented in hardware via semiconductor devices, chips, logical gates,circuits, circuit cards, and/or other physical hardware devices in lieuof, or in addition to, a processor-based system. In an embodiment, maskpattern module 1130 and a scan pattern test file 1132 may include datain addition to instructions or statements.

The computer system 1100 may include a bus interface unit 1109 to handlecommunications among the processor 1102, the memory 1104, a displaysystem 1124, and the I/O bus interface unit 1110. The I/O bus interfaceunit 1110 may be coupled with the I/O bus 1108 for transferring data toand from the various I/O units. The I/O bus interface unit 1110communicates with multiple I/O interface units 1112, 1114, 1116, and1118, which are also known as I/O processors (IOPs) or I/O adapters(IOAs), through the I/O bus 1108. The display system 1124 may include adisplay controller, a display memory, or both. The display controllermay provide video, audio, or both types of data to a display device1126. The display memory may be a dedicated memory for buffering videodata. The display system 1124 may be coupled with a display device 1126,such as a standalone display screen, computer monitor, television, or atablet or handheld device display. In an embodiment, the display device1126 may include one or more speakers for rendering audio.Alternatively, one or more speakers for rendering audio may be coupledwith an I/O interface unit. In alternate embodiments, one or more of thefunctions provided by the display system 1124 may be on board anintegrated circuit that also includes the processor 1102. In addition,one or more of the functions provided by the bus interface unit 1109 maybe on board an integrated circuit that also includes the processor 1102.

The I/O interface units support communication with a variety of storageand I/O devices. For example, the terminal interface unit 1112 supportsthe attachment of one or more user I/O devices 1120, which may includeuser output devices (such as a video display device, speaker, and/ortelevision set) and user input devices (such as a keyboard, mouse,keypad, touchpad, trackball, buttons, light pen, or other pointingdevice). A user may manipulate the user input devices using a userinterface, in order to provide input data and commands to the user I/Odevice 1120 and the computer system 1100, and may receive output datavia the user output devices. For example, a user interface may bepresented via the user I/O device 1120, such as displayed on a displaydevice, played via a speaker, or printed via a printer.

The storage interface 1114 supports the attachment of one or more diskdrives or direct access storage devices 1122 (which are typicallyrotating magnetic disk drive storage devices, although they couldalternatively be other storage devices, including arrays of disk drivesconfigured to appear as a single large storage device to a hostcomputer, or solid-state drives, such as flash memory). In anotherembodiment, the storage device 1122 may be implemented via any type ofsecondary storage device. The contents of the memory 1104, or anyportion thereof, may be stored to and retrieved from the storage device1122 as needed. The I/O device interface 1116 provides an interface toany of various other I/O devices or devices of other types, such asprinters or fax machines. The network interface 1118 provides one ormore communication paths from the computer system 1100 to other digitaldevices and computer systems; these communication paths may include,e.g., one or more networks 1140.

Although the computer system 1100 shown in FIG. 11 illustrates aparticular bus structure providing a direct communication path among theprocessors 1102, the memory 1104, the bus interface 1109, the displaysystem 1124, and the I/O bus interface unit 1110, in alternativeembodiments the computer system 1100 may include different buses orcommunication paths, which may be arranged in any of various forms, suchas point-to-point links in hierarchical, star or web configurations,multiple hierarchical buses, parallel and redundant paths, or any otherappropriate type of configuration. Furthermore, while the I/O businterface unit 1110 and the I/O bus 1108 are shown as single respectiveunits, the computer system 1100 may, in fact, contain multiple I/O businterface units 1110 and/or multiple I/O buses 1108. While multiple I/Ointerface units are shown, which separate the I/O bus 1108 from variouscommunications paths running to the various I/O devices, in otherembodiments, some or all of the I/O devices are connected directly toone or more system I/O buses.

In various embodiments, the computer system 1100 is a multi-usermainframe computer system, a single-user system, or a server computer orsimilar device that has little or no direct user interface, but receivesrequests from other computer systems (clients). In other embodiments,the computer system 1100 may be implemented as a desktop computer,portable computer, laptop or notebook computer, tablet computer, pocketcomputer, telephone, smart phone, or any other suitable type ofelectronic device.

FIG. 11 is intended to depict the representative major components of thecomputer system 1100, according to various embodiments. Individualcomponents, however, may have greater complexity than represented inFIG. 11, components other than or in addition to those shown in FIG. 11may be present, and the number, type, and configuration of suchcomponents may vary. Several particular examples of additionalcomplexity or additional variations are disclosed herein; these are byway of example only and are not necessarily the only such variations.The various program components illustrated in FIG. 11 may beimplemented, in various embodiments, in a number of different manners,including using various computer applications, routines, components,programs, objects, modules, data structures, etc., which may be referredto herein as “software,” “computer programs,” or simply “programs.”

Referring back to FIG. 11, embodiments may be a system, a method, and/ora computer program product. The computer program product may include acomputer readable storage medium (or media) having computer readableprogram instructions thereon for causing a processor to carry outaspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

FIG. 12 shows a block diagram of an exemplary design flow 1200 used forexample, in semiconductor IC logic design, simulation, test, layout, andmanufacture. Design flow 1200 includes processes, machines and/ormechanisms for processing design structures or devices to generatelogically or otherwise functionally equivalent representations of thedesign structures and/or devices described above and shown in FIG. 1-11.The design structures processed and/or generated by design flow 1200 maybe encoded on machine-readable transmission or storage media to includedata and/or instructions that when executed or otherwise processed on adata processing system generate a logically, structurally, mechanically,or otherwise functionally equivalent representation of hardwarecomponents, circuits, devices, or systems. Machines include, but are notlimited to, any machine used in an IC design process, such as designing,manufacturing, or simulating a circuit, component, device, or system.For example, machines may include: lithography machines, machines and/orequipment for generating masks (e.g. e-beam writers), computers orequipment for simulating design structures, any apparatus used in themanufacturing or test process, or any machines for programmingfunctionally equivalent representations of the design structures intoany medium (e.g. a machine for programming a programmable gate array).

Design flow 1200 may vary depending on the type of representation beingdesigned. For example, a design flow 1200 for building an applicationspecific IC (ASIC) may differ from a design flow 1200 for designing astandard component or from a design flow 1200 for instantiating thedesign into a programmable array, for example a programmable gate array(PGA) or a field programmable gate array (FPGA) offered by Altera® Inc.or Xilinx® Inc.

FIG. 12 illustrates multiple such design structures including an inputdesign structure 1220 that is preferably processed by a design process1210. Design structure 1220 may be a logical simulation design structuregenerated and processed by design process 1210 to produce a logicallyequivalent functional representation of a hardware device. Designstructure 1220 may also or alternatively comprise data and/or programinstructions that when processed by design process 1210, generate afunctional representation of the physical structure of a hardwaredevice. Whether representing functional and/or structural designfeatures, design structure 1220 may be generated using electroniccomputer-aided design (ECAD) such as implemented by a coredeveloper/designer. When encoded on a machine-readable datatransmission, gate array, or storage medium, design structure 1220 maybe accessed and processed by one or more hardware and/or softwaremodules within design process 1210 to simulate or otherwise functionallyrepresent an electronic component, circuit, electronic or logic module,apparatus, device, or system such as those shown in FIG. 1-11. As such,design structure 1220 may comprise files or other data structuresincluding human and/or machine-readable source code, compiledstructures, and computer-executable code structures that when processedby a design or simulation data processing system, functionally simulateor otherwise represent circuits or other levels of hardware logicdesign. Such data structures may include hardware-description language(HDL) design entities or other data structures conforming to and/orcompatible with lower-level HDL design languages such as Verilog andVHDL, and/or higher level design languages such as C or C++.

Design process 1210 preferably employs and incorporates hardware and/orsoftware modules for synthesizing, translating, or otherwise processinga design/simulation functional equivalent of the components, circuits,devices, or logic structures shown in FIG. 1-FIG. 11 to generate aNetlist 1280 which may contain design structures such as designstructure 1220. Netlist 1280 may comprise, for example, compiled orotherwise processed data structures representing a list of wires,discrete components, logic gates, control circuits, I/O devices, models,etc. that describes the connections to other elements and circuits in anintegrated circuit design. Netlist 1280 may be synthesized using aniterative process in which netlist 1280 is resynthesized one or moretimes depending on design specifications and parameters for the device.As with other design structure types described herein, netlist 1280 maybe recorded on a machine-readable data storage medium or programmed intoa programmable gate array. The medium may be a non-volatile storagemedium such as a magnetic or optical disk drive, a programmable gatearray, a compact flash, or other flash memory. Additionally, or in thealternative, the medium may be a system or cache memory, buffer space,or electrically or optically conductive devices and materials on whichdata packets may be transmitted and intermediately stored via theInternet, or other networking suitable means.

Design process 1210 may include hardware and software modules forprocessing a variety of input data structure types including Netlist1280. Such data structure types may reside, for example, within libraryelements 1230 and include a set of commonly used elements, circuits, anddevices, including models, layouts, and symbolic representations, for agiven manufacturing technology (e.g., different technology nodes, 22 nm,32 nm, 45 nm, 120 nm, etc.). The data structure types may furtherinclude design specifications 1240, characterization data 1250,verification data 1260, design rules 1270, and test data files 1285which may include input test patterns, output test results, and othertesting information. Design process 1210 may further include, forexample, standard mechanical design processes such as stress analysis,thermal analysis, mechanical event simulation, process simulation foroperations such as casting, molding, and die press forming, etc. One ofordinary skill in the art of mechanical design can appreciate the extentof possible mechanical design tools and applications used in designprocess 1210 without deviating from the scope and spirit of theinvention. Design process 1210 may also include modules for performingstandard circuit design processes such as timing analysis, verification,design rule checking, place and route operations, etc.

Design process 1210 employs and incorporates logic and physical designtools such as HDL compilers and simulation model build tools to processdesign structure 1220 together with some or all of the depictedsupporting data structures along with any additional mechanical designor data (if applicable), to generate a second design structure 1290.Design structure 1290 resides on a storage medium or programmable gatearray in a data format used for the exchange of data of mechanicaldevices and structures (e.g. information stored in a IGES, DXF,Parasolid XT, JT, DRG, or any other suitable format for storing orrendering such mechanical design structures). Similar to designstructure 1220, design structure 1290 preferably comprises one or morefiles, data structures, or other computer-encoded data or instructionsthat reside on transmission or data storage media and that whenprocessed by an ECAD system generate a logically or otherwisefunctionally equivalent form of one or more of the embodiments of theinvention shown in FIG. 1-11. In one embodiment, design structure 1290may comprise a compiled, executable HDL simulation model thatfunctionally simulates the devices shown in FIG. 1-11.

Design structure 1290 may also employ a data format used for theexchange of layout data of integrated circuits and/or symbolic dataformat (e.g. information stored in a GDSII (GDS2), GL1, OASIS, mapfiles, or any other suitable format for storing such design datastructures). Design structure 1290 may comprise information such as, forexample, symbolic data, map files, test data files, design contentfiles, manufacturing data, layout parameters, wires, levels of metal,vias, shapes, data for routing through the manufacturing line, and anyother data required by a manufacturer or other designer/developer toproduce a device or structure as described above and shown in FIG. 1-11.Design structure 1290 may then proceed to a stage 1295 where, forexample, design structure 1290: proceeds to tape-out, is released tomanufacturing, is released to a mask house, is sent to another designhouse, is sent back to the customer, etc.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method of masking scan channels in asemiconductor chip, comprising storing, in a first memory of a firstmask logic, a first channel mask enable decode for a first mask thatmasks a first scan channel of a circuit under test; storing, in a secondmemory of a first mask logic, a second channel mask enable decode for asecond mask that masks a second scan channel of the circuit under test;receiving at least three channel mask enable signals, a first channelmask enable signal on a first channel mask enable pin, a second channelmask enable signal on a second channel mask enable pin, and a thirdchannel mask enable signal on a third channel mask enable pin, whereinthe first, second, and third channel mask enable signals produce achannel mask enable encode; comparing with a first comparator the firstchannel mask enable decode to the channel mask enable encode; comparingwith a second comparator the second channel mask enable decode to thechannel mask enable encode; masking the first scan channel with thefirst mask when the first channel mask enable decode matches the channelmask enable encode; and masking the second scan channel with the secondmask when the second channel mask enable decode matches the channel maskenable encode.
 2. The method of claim 1, further comprising: masking ascan pattern output signal of a first hierarchal test block (HTB) havinga plurality of scan channels, the scan channels have a scan channelinput and a scan channel output, the scan channel input receives a scantest pattern, the scan channel output provides a scan pattern outputsignal, with the first mask logic when one of the first and second masksare enabled.
 3. The method of claim 2, wherein the scan channel input isthe same across all scan channels.
 4. The method of claim 1, furthercomprising: storing in a third memory of a second mask logic a thirdchannel mask enable decode for the first mask that masks a first scanchannel of a second HTB having a plurality of scan channels; storing ina fourth memory of a second mask logic a fourth channel mask enabledecode for the second mask that masks a second scan channel of thesecond HTB; receiving the channel mask enable encode; comparing with athird comparator the third channel mask enable decode to the channelmask enable encode; comparing with a fourth comparator the fourthchannel mask enable decode to the channel mask enable encode; maskingthe first scan channel of the second HTB with the first mask when thethird channel mask enable decode matches the channel mask enable encode;and masking the second scan channel of the second HTB with the secondmask when the second channel mask enable decode matches the channel maskenable encode.
 5. The method of claim 4, further comprising: receiving asorted and combined scan pattern test file of test patterns of the firstHTB and test patterns of the second HTB that run on the circuit undertest, the scan pattern test file configured by: determining a maximumnumber of channel mask enable encodes on the semiconductor chip;determining a maximum number of channel mask enable encodes used for thefirst HTB and the second HTB; sorting the test patterns used to test thefirst HTB and second HTB into one or more mask sets dependent on thenumber of masks each test pattern needs, the mask sets increase in masknumber from a zero mask set to the maximum number of channel mask enableencodes used for the respective HTBs; and combining test patterns of themask sets of the first HTB and the second HTB to be performed in a sametest pattern, wherein the number of masks per test pattern of thecombined mask sets is no more than the maximum number of channel maskenable encodes on the semiconductor chip.
 6. The method of claim 1,wherein the first scan channel is masked by the first mask and thesecond mask.
 7. The method of claim 1, further comprising: masking allscan channels of the semiconductor chip when the channel mask enableencode signals a mask all channel mask enable encode.
 8. The method ofclaim 1, further comprising: masking none of the scan channels of thesemiconductor chip when the channel mask enable encode signals a no maskchannel mask enable encode.